1. Field of the Invention
The present invention relates to a structure for a circuit board attaching portion.
2. Description of the Related Art
An instrument having a speedometer, a tachometer, a fuel gauge, a water temperature gauge, and the like is attached in a vehicle such as an automobile.
Such an instrument has a structure shown in FIG. 4. A dial plate 3 in which a letter/scale portion is formed along an area where each of pointers 2 is swung is attached to a surface of a mounting part 1 such as a case. A circuit board 5 having circuit components such as movements 4 for swinging the pointers 2 is attached to the rear face of the mounting part 1 such as a case.
Engaged portions 7 such as engagement holes 6 or engagement notches are formed in the circuit board 5. Engagement claws 8 protrude from the mounting part 1. As shown in FIGS. 5A to 5C, the engagement claws 8 are engaged with the engaged portions 7, respectively, to attach the circuit board 5 to the mounting part 1.
In FIG. 4, the reference numeral 9 denotes a light guide plate which guides light emitted from a light source (not shown) to the letter/scale portions of the dial plate 3, base portions of the pointers 2, and the like. Reference numeral 10 denotes electrical connecting pins which elongate from the movements 4. Reference numeral 11 denotes solder for electrically connecting the electrical connecting pins 10 to the circuit board 5.
In the structure for the circuit board attaching portion according to the related art, usually, the engaged portions 7 of the circuit board 5 are formed by a punching operation in press working, and hence edge portions have acute angles. Moreover, the mounting part 1 such as a soft case, which is produced by, for example, injection-molding a PP composite material, is different in hardness from the hard circuit board 5, which is formed by stacking an epoxy resin, a paper phenol resin, and the like. Because of these reasons, when the engagement claws 8 are engaged with the engaged portions 7, a catch due to, for example, a bite between the edge portion of the engaged portion 7 and an inclined guide face, which is formed in a tip end of the engagement claws 8 occurs as shown in FIG. 6. This impairs the efficiency of the attaching work. There arises the possibility that, during the attaching work, this catch causes the harder circuit board 5 to crack or whittling to be produced.
It is an object of the invention to provide a structure for a circuit board attaching portion in which the above-discussed problem can be solved, the efficiency of the attaching work can be improved, and the circuit board 5 can be prevented from cracking.
In order to attain the object, according to a first aspect of the invention, there is provided a structure for a circuit board attaching portion including a circuit board on which an engaged portion are formed and a mounting part in which an engaging claw are formed. The circuit board is attached to the mounting part by engaging the engaging claw with the engaged portion. A catch preventing portion, which prevents the engaging claw from being caught, is formed on a side of a mounting part attached face of the engaged portion.
According to the first aspect of the invention, the catch preventing portion is formed on a side of a mounting part attached face of the engaged portion. Even when an edge portion of the engaged portion has an acute angle or even when there is a difference in hardness between the circuit board and the mounting part, the catch preventing portion effectively prevents a catch between the engaged portion and the engagement claw from occurring. Therefore, the efficiency of the attaching work can be improved and the circuit board can be prevented from cracking.
According to a second aspect of the invention, the catch preventing portion is an edge dulling portion, which is formed on an edge portion of the engaged portion.
According to the second aspect of the invention, since the edge dulling portion is formed as the catch preventing portion on the edge portion of the engaged portion, it is possible to prevent more effectively a catch between the engaged portion and the engagement claw from occurring.
According to a third aspect of the invention, the edge dulling portion is a building up portion, which is formed on the edge portion of the engaged portion.
According to the third aspect of the invention, since the building up portion is formed as the edge dulling portion on the edge portion of the engaged portion, the edge portion of the engaged portion can be dulled so that a catch between the engaged portion and the engagement claw can be prevented more effectively from occurring.
According to a fourth aspect of the invention, the building up portion is solder.
According to the fourth aspect of the invention, since the building up portion is the solder, the edge portion of the engaged portion can be easily dulled so that a catch between the engaged portion and the engagement claw can be effectively prevented from occurring.
According to a fifth aspect of the invention, the solder is disposed on a land, which is formed on the edge portion of the engaged portion.
According to the fifth aspect of the invention, since the solder is disposed on a land, which is formed on the edge portion of the engaged portion, the solder can be effectively disposed.
According to a sixth aspect of the invention the solder is formed concurrently with soldering of a circuit component onto the circuit board.
According to the sixth aspect of the invention, since the solder of the building up portion is formed concurrently with soldering of a circuit component onto the circuit board, it is not required to particularly form the catch preventing portion and hence the production cost can be suppressed.